Frequency of recurrence is one of the major problems in cancer treatment Relapse from clinically undetectable residual disease is the most likely mechanism. Detection of minimal disease is extremely difficult since tumor specific markers are not readily available. Molecular technology has provided a means to demonstrate residual disease by identifying clonal rearrangement patterns that are present in malignant hematopoietic cells (1). Southern blot hybridization detects neoplastic cells at levels as low as 1% of the total number of cells (2). However, one of the major drawbacks in this situation is that it is difficult to be certain that faint nongermline bands indeed represent clonal rearrangements Furthermore, no rearranged bands can be detected in cases in which the concentration of neoplastic cells is below 1%. Theoretically this occurs frequently while patients are in remission.
The karyotypic abnormality, t(14;18)(q32;q21), has been observed in approximately 90% of human follicular lymphomas (3-5). This translocation frequently results in rearrangement of a putative oncogene "bc1-2" which resides at chromosome 18 band q21 (6). In the majority of cases with the t(14;18), the molecular breakpoints on chromosome 18q21 cluster within a 4.3 kilobase (kb) Hind III restriction fragment or more specifically a 2.8 kb EcoR1-Hind III restriction fragment which has recently been designated the t(14;18) major breakpoint cluster region (mbr) (7-11). DNA sequencing of the crossover sites revealed that breakpoints on chromosome 18q21 were clustered within 150 base pairs (bp) of each other and breakpoints on chromosome 14 were located close to the 5' end of one of the joining (J) segments (J1 to J6) of the immunoglobulin heavy chain locus (JH) (11-13).
Saiki et al. have recently utilized a new technique, sequence amplification by polymerase chain reaction (PCR), to diagnose sickle cell anemia prenatally (14). This technique is mainly applicable to genetic disorders with a point DNA mutation. It is difficult to apply PCR to the detection of chromosomal translocation because of the variability of molecular breakpoints on chromosomes. The present invention describes a method of utilizing the PCR technique to amplify DNA sequences flanking the crossover site of a chromosomal translocation such as t(14;18) which is characteristic of a tumor. Since cells carrying the subject t(4;18) translocation are unique to malignant hematopoietic cells, detection and amplification of such sequences can be used as evidence for minimal residual disease. The present invention also demonstrates the unique consequence of applying the PCR technique to a chromosomal translocation, i.e., preferential amplification of the hybrid DNA sequences of the chromosomal translocation, but not the normal DNA sequence.